I recently purchased a "matched" quad of KT150 tubes from a well known, seemingly well respected tube vendor. My goal is not to bash him, but to educate myself. One of the "matched" tubes has a transconductance 20% under the average of the other three tubes. When I called to ask about that, I was told transconductance is not a critical factor when matching these tubes for an AR amp. That bias current is the critical factor for tube matching in this particular situation. True? False?
KT150 Tube Matching
Ok. Educate me. I don't know enough to even be dangerous. What are the critical factors used when matching a set of KT150 tubes, say, to go in an Audio Research amp? Transconductance? Bias current draw? A combination of the two? Is there any spec. or threshold on the variations? Does Audio Research do anything special to match their replacement tube sets?